1. Field of the Invention
The present invention relates to deep-colored fibers, particularly, those having an excellent deep-color durability and a process for manufacturing the same.
2. Description of the Prior Art
The study for providing synthetic fibers and natural fibers with a vivid and deep color has hitherto been extensively carried out and improvements aiming at the so-called "raven black", for example, have been proposed.
In Journal of the Textile Machinery Society of Japan, Vol. 22, (No. 5) pp. 360.about.368 (May, 1969) and British Patent No. 1,199,385, there are seen early disclosures of an optical color improvement performable by roughening fiber surfaces to an adequate ruggedness. Further, Japanese Patent Application Laid-open No. 52-99,400 proposed deep-colored fibers having fine recesses an projections of specified shapes on the surfaces thereof. However, in the processes to produce such fibers, the fibers' own surfaces are etched so that difficulties have been encountered such as a low etching rate, color fading due to abrasion of too fine and numerous recesses and projections, decomposition of dyes, lowering of color fastness, hard control of etching conditions, or the like. In addition, many problems have been posed in the practical use, such as poor development of the color deepening effect, or the like, attributable to a refractive index of a surface layer of the fiber that is same as that of the material of the fiber or increased as the density increases. Alternatively, color-deepening finishing processes have so far been carried out by treating with various finishing agents to form low refractive surface layers, such as fluoro-chemical finishes, silicone finishes, polyurethane finishes, or the like. Though these processes are simple, convenient and industrially feasible without requiring any special equipments, yet difficulties in uniform application to the fiber surfaces of the finishing agents, deterioration of the hand and color shade, lowering of color-fastness, etc. are unavoidable. Moreover, with respect to color-deepening performances, there are questions of deficiency as only the prevention of reflection is effected by low refractive indices of the finishing agents.
Japanese Patent Application Laid-open No. 55-107,512 is directed to a process wherein polyester itself is admixed with alkali-soluble fine particles, e.g., fine grain silica, and after spinning into fibers, recesses are formed on the fiber surfaces by eluting these particles with an alkaline solution. According to this process, since the particles are so fine and uniformly dispersed that the elution progresses simultaneously at extremely numerous and very closely adjacent portions, a great number of fine recesses and projections are formed. However, this process cannot form well-defined recesses or projections having acute-angled edges. Therefore, the color-deepening effect has not been satisfactory.
U.S. Pat. No. 4,400,424 has proposed good durable deep-colored fibers having smooth surfaces that are produced by filling up recesses on the surfaces of the fibers with a resin having a low refractive index. However, according to this process, it is difficult to form specified recesses on the surfaces of the fibers, particularly, natural fibers. Even if the recesses could be formed, the development of deep color would be poor since the fiber surfaces had been smoothed by filling up the recesses with the resin. Namely, in this reference, a study was conducted in a region where an L-value of fabrics before a rubbing test was between 11 and 13 that could not be said to be "raven black". Further, the recesses and projections are formed on the fiber itself through a plasma etching treatment, which are caused by a higher order structure such as crystals in the fiber, size and arrangement of amorphous regions and the like. Therefore, only recesses and projections very small in size and uniform in shape and arrangement are provided as disclosed by the above reference or Japanese Patent Application Publication No. 11,709/1984. From the above reasons, the color-deepening performances are not sufficient. As for fastness to crocking, what is liable to abrasion is the resin that is adhered on the fiber; rather than the fiber itself that has been drawn to orient and crystallize its molecules considerably. Therefore, it is necessary to employ selectively an abrasion resistant resin that is excellent in mechanical properties and affinity for the fiber.
In Japanese Patent Application Laid-open No. 61-97,490, 60-224,878 or others, there have been proposed processes for providing polyester fibers with a deep color by applying a silicone resin to the polyester fibers followed by a plasma treatment. According to these processes, etching conditions are no good such that the etching rate of the silicone resin finishing agent covering the fibers is too low to form well-defined recesses and projections. Accordingly, these processes cannot provide industrially advantageously fibers with an improved color-deepening property or durable deep color. Additionally, another problem is that a great number of recesses and projections having a simple and uniform shape are formed, so that these fine and simply shaped recesses and projections would be readily fractured due to friction during washing or a normal use, causing partial impairment of the color-deepening property, resulting in deterioration of the quality such as uneven color, undesirable glaze of fabrics, or the like.
Japanese Patent Application Laid-open No. 60-17,190 has proposed a process wherein a resinous film having differentiated resistances for plasma etching is formed on fiber surfaces and many fine recesses and projections are formed on the surface of the resinous film by a plasma treatment. Preferable films comprise inorganic fine particles and a resin that is excellent in compatibility therewith and in uniform covering property, or a cationic polyurethane and/or a vinylpolymer-modified cationic polyurethane having a refractive index of not exceeding 1.5. In the above proposal, the recesses and projections formed on the surfaces of the resinous film are small in size and large in number so that problems similar to the aforementioned still exist.
U.S. Pat. No. 4,522,873 has proposed a process for producing deep-colored fibers wherein fibers are subjected to a film-forming treatment with an agent comprising a silicone resin and inorganic fine particles admixed therewith, followed by a plasma treatment. This proposed process is also involved in problems such as a low etching rate, uneven etching caused by uneven distribution of the fine particles adhered on the fiber surfaces, change in performance caused by falling-off of the fine particles, or the like.
As mentioned above, the conventional color-deepened fibers have had drawbacks such as an insufficient depth of color, insufficient durability, low rate of color-deepening treatment, or the like.